The invention concerns a diffractively and/or refractively operating optical apparatus for passing incident light, preferably sunlight, on to a receiver, preferably on to a solar element. The optical apparatus includes a tracking device which is controlled based on the variation with respect to time of the relative position of the light source and the receiver, preferably based on the position of the sun.
Optical apparatuses that track the direction of sunlight are used in solar installations. They are associated with the solar elements, to make the most efficient possible use of the sunlight; in order to direct the incident sunlight on to the solar element on an angle as close to perpendicular as possible. In the practical context of solar engineering, this is accomplished by using focusing systems with lenses and parabolic mirrors, which suitably deflect and concentrate the light. In order to achieve an optimum effect, these systems track the movement of the sun. This requires large and expensive tracking devices, which precisely control the position of these generally bulky and heavy optical apparatuses.
A press release in the newspaper “Frankfurter Allgemeine Zeitung,” supplement No. 144 of 28th Jul. 1994, contained a report about the use of holographic foil for applying sunlight to solar cells. The holographic foil is intended to replace conventional prisms and lenses. The foil divides up the light spectrum and directs the divided up light to solar cells, which are specifically designed for the respective spectral range.
DE 31 41 789 A1 discloses a sun ray concentrator having a body which is in the form of a prism and has a material layer with a hologram structure on the entrance face and on the reflection face. The parameters of the hologram structure are so selected that the radiation is passed by means of the hologram into the prism where it is redirected in such a way that it issues focused at a plurality of end faces of the prism. In that situation, the radiation is concentrated and at the same time the arrangement provides for division into the various spectral ranges, with concentration of the various spectral ranges on the various ray exit faces. This allows light to be directed to specific photoconverters for the respective spectral range. However, the sun ray concentrator consisting of prisms suffers from the above-described disadvantages in terms of tracking. In addition, because of the prisms, shadow effects occur which reduce the conversion rate.
U.S. Pat. No. 4,054,356 A1 discloses a sun ray concentrator which is in the form of a hologram of a light spot source. The focal point of the hologram lens, however, is found to be so large that, for the purposes of arranging a receiver for concentrated radiation at the focal point of the lens, an auxiliary device connecting the receiver to the lens is required. In addition, this arrangement involves irregular distribution of energy at the surface of the receiver.
DE 30 12 500 A1 discloses a retroreflector for use in light barriers and light curtains. The reflector uses diffraction gratings which are formed by holographic procedures in a photosensitive material. When the reflector is illuminated, the radiation impinging thereon is reflected and focused outside the reflector plate with the hologram.